Multibridge power converter with multiple outputs

Abstract

According to one aspect of the present disclosure, there is provided a power converter apparatus that includes at least two switching bridges connected to a Direct Current (DC) bus and both generating pulse-width-modulated (PWM) voltages to non-isolated outputs, and an isolation transformer having a primary winding connected across the outputs of the two switching bridges and a secondary winding connected to isolated outputs. In a non-isolated mode, the two switching bridges are configured to operate in a parallel mode, and power is transferred between the DC bus and the non-isolated outputs. In an isolated mode, the two switching bridges are configured to operate in a full bridge mode, and power is transferred between the DC bus and the isolated outputs through the transformer.

What is claimed is: 
     
       1. A power converter apparatus comprising:
 a Direct Current (DC) bus configured to be connected to a power source; 
 a first switching bridge and a second switching bridge, both connected to the DC bus and generating pulse-width-modulated (PWM) voltages to non-isolated outputs of the first switching bridge and the second switching bridge; and 
 a transformer having a primary winding connected across the non-isolated outputs of the first switching bridge and the second switching bridge and having a secondary winding connected to isolated outputs, wherein: 
 in a non-isolated mode, the first switching bridge and the second switching bridge are controlled to operate in a parallel mode, and power is transferred between the DC bus and a non-isolated load coupled to the non-isolated outputs and power bypasses the transformer due to the parallel operation of the first switching bridge and the second switching bridge; and 
 in an isolated mode, the first switching bridge and the second switching bridge are controlled to operate in a full bridge mode, and power is transferred between the DC bus and a load coupled to the isolated outputs through the transformer. 
 
     
     
       2. The apparatus of  claim 1 , wherein a controller, operating the first switching bridge and the second switching bridge with PWM synchronization and/or phase shifting according to at least two different operation modes:
 in the non-isolated mode, the two switching bridges are controlled with PWM switching signals which are synchronized in phase; and 
 in the isolated mode, the two switching bridges are controlled with PWM switching signals which are phase shifted. 
 
     
     
       3. The apparatus of  claim 1 , wherein at least one transformer disconnect switch is connected in series with the isolation transformer winding, either on the primary side or on the secondary side, and operated according to at least two different operation modes:
 in the non-isolated mode, the transformer disconnect switch remains open and the two switching bridges are controlled with PWM switching signals which are interleaved with a phase shift angle to increase the effective PWM switching frequency across the non-isolated outputs; and 
 in the isolated mode, the transformer disconnect switch remains closed and the two switching bridges are controlled in a full bridge mode. 
 
     
     
       4. The apparatus of  claim 1 , wherein the switching bridges use two-level, three-level, five-level, or any multilevel converter topologies, such as diode neutral-point-clamp (NPC) multilevel converter, active NPC (ANPC) multilevel converter, flying-capacitor multilevel converter, or a combination of any different multilevel topologies between the switching bridges. 
     
     
       5. The apparatus of  claim 1 , wherein the power converter includes three, four or any higher number of switching bridges, either connected to multiple separate isolation transformers, or to the same isolation transformer with multiple windings that are coupled together, or to a mixture of different transformer configurations. 
     
     
       6. The apparatus of  claim 1 , further configured as a non-isolated PWM inverter integrated with an isolated battery charging system, including:
 a battery of many battery cells connected to the DC bus through a main contactor or a switch; 
 two or more pairs of converter bridges to form a DC-to-AC inverter and generate PWM voltages to non-isolated outputs; and 
 one or more isolation transformers, having primary windings connected across the outputs of each pair of converter bridges and having secondary windings connected to power converters of any type to produce a DC voltage to charge the battery, wherein: 
 during inverter operation in the non-isolated mode, the battery main contactor is closed, within each pair of converter bridges the two switching bridges are operated in a parallel mode; and 
 during battery charging operation in the isolated mode, the battery main contactor is open, within each pair of converter bridges the two switching bridges are operated in a full bridge mode. 
 
     
     
       7. The apparatus of  claim 6 , wherein the PWM inverter non-isolated outputs provide power to drive an AC motor with two or more sets of motor windings which are separate from one another; and, during battery charging operation in the isolated mode, additional PWM gate switching synchronization is applied among those switching bridges connected across the same set of motor windings, therefore each set of motor windings are excited with virtually zero differential voltages across the motor terminals in order to reduce any unintended motor circulating currents. 
     
     
       8. The apparatus of  claim 6 , wherein an AC source is connected to the DC bus indirectly through an AC-to-DC rectifier; and, the AC-to-DC rectifier is integrated with, and its power-factor-correction function realized by, operating part or whole pairs of the inverter switching bridges in reverse power direction to draw power from the AC source, with or without using the motor windings as inductors required by the rectifier. 
     
     
       9. The apparatus of  claim 1 , further configured as a non-isolated DC Boost converter integrated with an isolated battery charging system, including:
 one or more pairs of switching bridges formed as a DC-to-DC Boost converter, with non-isolated outputs connected to a battery through a main contactor switch and one or more inductors, and with inputs connected to the DC bus; and 
 an isolation transformer, having primary windings connected across the non-isolated outputs of the switching bridges and secondary windings connected to isolated outputs, wherein the isolated outputs are coupled to a power converter to produce a DC voltage for charging the battery; wherein: 
 during DC Boost operation in the non-isolated mode, the battery main contactor is closed, within the switching bridges controlled to operate in a parallel mode, wherein power is transferred from the battery to an AC load through an inverter coupled to the inputs of the switching bridges; and 
 during battery charging operation in the isolated mode, the battery main contactor is opened, with the switching bridges controlled to operate in a full bridge mode, wherein power is transferred from the DC bus to the battery through the isolation transformer and the power converter. 
 
     
     
       10. The apparatus of  claim 9 , further comprising a PWM inverter connected to the DC bus which drives an AC motor, wherein, the PWM inverter is operated in reverse power flow as a PFC rectifier to draw power from an AC source, with or without using the AC motor windings as inductors required by the rectifier. 
     
     
       11. A method of designing a power converter, comprising:
 receiving a power source to a Direct Current (DC) bus; 
 forming a pair of two switching bridges, both connected to the DC bus and generating pulse-width-modulated (PWM) voltages to non-isolated outputs of the two switching bridges; 
 placing a transformer, having a primary winding connected across the non-isolated outputs of the two switching bridges and having a secondary winding connected to isolated outputs, wherein, 
 in a non-isolated mode, operating the two switching bridges in a parallel mode wherein power is transferred between the DC bus and a non-isolated load coupled to the non-isolated outputs and power bypasses the transformer due to the parallel operation of the two switching bridges; and, 
 in an isolated mode, operating the two switching bridges in a full bridge mode wherein power is transferred between the DC bus and a load coupled to the isolated outputs through the transformer. 
 
     
     
       12. The method of  claim 11 , further comprising, designing a controller, operating the two switching bridges according to at least two different operation modes:
 in the non-isolated mode, operating the two switching bridges with PWM switching signals which are synchronized in phase; and, 
 in the isolated mode, operating the two switching bridges with PWM switching signals which are phase-shifted. 
 
     
     
       13. The method of  claim 11 , further comprising, connecting at least one disconnect switch in series with the isolation transformer winding, either on the primary side or on the secondary side, wherein,
 in the non-isolated mode, keeping the transformer disconnect switch open, operating the two switching bridges in a parallel mode, synchronizing the PWM switching signals between the two bridges and interleaving the PWM signals with a phase shift angle, such that the effective PWM switching frequency is increased across the non-isolated outputs; and, 
 in the isolated mode, keeping the transformer disconnect switch closed, operating the two switching bridges in a full bridge mode, phase-shifting the PWM switching signals to be out of phase between the two bridges, so that power is transferred between the DC bus and the isolated outputs through the transformer. 
 
     
     
       14. The method of  claim 11 , wherein, designing the switching bridges using two-level, three-level, five-level, or any multilevel converter topologies, such as diode neutral-point-clamp (NPC) multilevel converter, active NPC (ANPC) multilevel converter, flying-capacitor multilevel converter, or a combination of any different multilevel topologies between the switching bridges. 
     
     
       15. The method of  claim 11 , wherein, configuring the power converter with three, four or any higher number of switching bridges, either connecting to multiple separate isolation transformers, or to the same isolation transformer with multiple windings that are coupled together, or to a mixture of different transformer configurations. 
     
     
       16. An electric vehicle, comprising:
 at least two power converter apparatuses according to  claim 1 ; 
 a battery coupled to the isolated outputs of the at least two power converter apparatuses, wherein the battery is coupled to the DC bus via a main contactor during the non-isolated mode. 
 
     
     
       17. The electric vehicle of  claim 16 , wherein inverter operation is performed in the non-isolation mode, the non-isolated outputs of the at least two power converter apparatuses provide power to drive an AC motor with two or more sets of motor windings which are separate from one another; and wherein during battery charging operation in the isolated mode, additional PWM gate switching synchronization is applied among the switching bridges of the at least two power converter apparatuses connected across the same set of motor windings, such that each set of motor windings are excited with virtually zero differential voltages across the motor terminals in order to reduce any unintended motor circulating currents. 
     
     
       18. An electric vehicle, comprising:
 a first switching bridge and a second switching bridge, both connected to a DC bus and generating pulse-width-modulated (PWM) voltages to non-isolated outputs, to form a DC-to-DC Boost converter, with the non-isolated outputs connected to a battery through a main contactor and one or more inductors; and 
 an isolation transformer, having a primary winding connected across the non-isolated outputs of the switching bridges and a secondary winding connected to isolated outputs, wherein the isolated outputs are coupled to a power converter to produce a DC voltage across the battery terminals, wherein: 
 during DC Boost operation in a non-isolated mode, the battery main contactor is closed, switching bridges are controlled to operate in a parallel mode, wherein power is transferred from the battery to the DC bus; and 
 during battery charging operation in an isolated mode, the battery main contactor is opened, the switching bridges are controlled to operate in a full bridge mode, wherein power is transferred from the DC bus to the battery through the isolation transformer and the power converter. 
 
     
     
       19. The electric vehicle of  claim 18  wherein the inductors are integrated in part or in whole into the isolation transformer design, and wherein the battery is connected through the main contactor to the middle point of the isolation transformer primary windings. 
     
     
       20. The electric vehicle of  claim 18  wherein the switching bridges use two-level, three-level, five-level, or any multilevel converter topologies, such as diode neutral-point-clamp (NPC) multilevel converter, active NPC (ANPC) multilevel converter, flying-capacitor multilevel converter, or a combination of any different multilevel topologies between the switching bridges, and wherein the power converter includes three, four or any higher number of switching bridges, either connected to multiple separate isolation transformers, or to the same isolation transformer with multiple windings that are coupled together, or to a mixture of different transformer configurations.